The present invention relates to an abnormality detecting apparatus for fuel vapor treating system, which adsorbs fuel vapor generated in a fuel tank with a canister and purges the adsorbed fuel vapor to an intake passage of an engine as necessary. The present invention also pertains to a method for controlling the abnormality testing apparatus.
A typical fuel vapor treating system has a canister that contains fuel adsorbent such as granular activated carbon. Fuel vapor generated in the fuel tank of a vehicle is guided to the canister by a vapor passage and is then adsorbed by the adsorbent in the canister. The adsorbed fuel vapor is purged to the intake passage of the engine through a purge line as necessary and is combusted in the engine. A purge control valve is located in the purge line to adjust the flow rate of the fuel vapor purged to the intake passage. The canister is communicated with the atmosphere by an atmosphere passage. A canister valve is located in the atmosphere passage to selectively expose the canister to the atmosphere. When the purge control valve and the canister valve are open, vacuum in the intake passage draws fuel vapor from the canister into the intake passage.
U.S. Pat. No. 5,263,462 discloses an apparatus for detecting abnormalities in a fuel vapor treating system like the one described above. The abnormality detecting apparatus seals a vapor zone including a fuel tank, a vapor passage, a canister, and a purge line, and checks whether fuel vapor is leaking from the vapor zone. Specifically, a purge control valve and a canister valve are closed immediately after the engine is stopped to seal the vapor zone. In this state, the detecting apparatus checks whether fuel vapor is leaking from the vapor zone based on the temperature and the pressure in the vapor zone. For example, if the pressure in the vapor zone sufficiently increases in accordance with an increase of the temperature in the vapor zone, the apparatus judges that fuel vapor is not leaking from the vapor zone. If the pressure in the vapor zone does not sufficiently increase in accordance with an increase of the temperature in the vapor zone, the apparatus judges that fuel vapor is leaking from the vapor zone, or that there is an abnormality in the fuel vapor treating system.
When the abnormality detecting procedure as described above is ended, the canister valve is opened so that the canister is exposed to the atmosphere.
At the time when the abnormality detecting procedure is finished, the pressure in the vapor zone can be higher than the atmospheric pressure. Therefore, when the canister valve is opened after the completion of the abnormality detecting procedure, air is discharged to the atmosphere due to the difference between the pressure in the vapor zone and the atmospheric pressure. The airflow discharges fuel vapor adsorbed by the adsorbent in the canister into the atmosphere.
The above problem is particularly remarkable in the abnormality detecting apparatus disclosed in U.S. Pat. No. 5,890,474. When executing the abnormality detecting procedure, the apparatus pressurizes a sealed vapor zone with a pressurizing pump after an engine is stopped. The apparatus judges whether fuel vapor is leaking from the vapor zone based on the increased pressure in the vapor zone. That is, if the pressure in the vapor zone is lower than a predetermined value despite the increase of the pressure in the sealed vapor zone, the apparatus judges that the fuel vapor is leaking from the vapor zone. In such an abnormality detecting apparatus, which has a pressurizing pump, the difference between the pressure in the vapor zone and the atmospheric pressure when the abnormality detection procedure is finished is greater than that of U.S. Pat. No. 5,263,462. Therefore, when the canister valve is opened after the abnormality detecting procedure is finished, air rushes out to the atmosphere from the canister. The airflow discharges fuel vapor adsorbed by the canister out to the atmosphere.
Accordingly, it is an objective of the present invention to provide an abnormality detecting apparatus used in a fuel vapor treating system, which apparatus prevents fuel vapor adsorbed by a canister from being discharged to the atmosphere. Another objective of the present invention is to provide a method for controlling the apparatus.
To achieve the foregoing and other objectives and in accordance with the purpose of the present invention, an abnormality detecting apparatus for a fuel vapor treating system is provided. The treating system includes a canister, which adsorbs fuel vapor generated in a fuel tank and purges the adsorbed fuel vapor to an intake passage of an engine. The detecting apparatus performs an abnormality detecting procedure for detecting an abnormality in the treating system. When performing the abnormality detecting procedure, the detecting apparatus seals a vapor zone, which includes the fuel tank and the canister, so that the pressure in the vapor zone exceeds the atmospheric pressure. The detecting apparatus determines whether fuel vapor is leaking from the vapor zone based on the pressure in the sealed vapor zone.
In one aspect of the present invention, the abnormality detecting apparatus includes a valve device and regulating means. The valve device selectively communicates the vapor zone with and disconnects the vapor zone from the atmosphere. During the abnormality detecting procedure, the valve device disconnects the vapor zone from the atmosphere. After the abnormality detecting procedure is ended, the valve device communicates the vapor zone with the atmosphere. When the valve device communicates the vapor zone with the atmosphere, the regulating means regulates a rate at which the pressure in the vapor zone is lowered.
In another aspect of the present invention, the abnormality detecting apparatus includes a canister valve and a controller. The canister valve selectively communicates the canister with and disconnects the canister from the atmosphere. The controller controls the canister valve. During the abnormality detection procedure, the controller shuts the canister valve to disconnect the vapor zone from the atmosphere. After the abnormality detecting procedure is ended, the controller controls the canister valve such that the canister valve communicates the vapor zone with the atmosphere and regulates the rate at which the vapor zone pressure is lowered.
In a further aspect of the present invention, the abnormality detecting apparatus includes a valve device and pressure lowering means. The valve device selectively communicates the vapor zone with and disconnects the vapor zone from the atmosphere. During the abnormality detecting procedure, the valve device disconnects the vapor zone from the atmosphere. After the abnormality detecting procedure is ended, the valve device communicates the vapor zone with the atmosphere. When the valve device communicates the vapor zone with the atmosphere, the pressure lowering means slowly lowers the pressure in the vapor zone to the atmospheric pressure, thereby preventing air released from the vapor zone to the atmosphere from separating fuel vapor from the canister.
The present invention may also be applied to a method for controlling an abnormality detecting apparatus for a fuel vapor treating system. The treating system includes a canister, which adsorbs fuel vapor generated in a fuel tank and purges the adsorbed fuel vapor to an intake passage of an engine. The method includes: sealing a vapor zone, which includes the fuel tank and the canister, so that the pressure in the vapor zone exceeds the atmospheric pressure; determining whether fuel vapor is leaking from the vapor zone based on the pressure in the sealed vapor zone, thereby detecting an abnormality of the treating system; communicating the vapor zone with the atmosphere after the abnormality detecting procedure is ended; and slowly lowering the pressure in the vapor zone to the atmospheric pressure when the vapor zone is communicated with the atmosphere, thereby preventing air released from the vapor zone to the atmosphere from separating fuel vapor from the canister.
Other aspects and advantages of the invention will become apparent from the following description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention.